Transcription
The translation was done by Dhuha Al-Jazmati. Follow us on Twitter and Facebook! (@AmoebaSisters) We have a riddle for you. Actually, it's not a riddle. We're not good at riddles. They are hints about our favorite molecule. It is polar. It is shaped like an elongated V. Its properties are amazing. We have a riddle for you. Actually, it's not a riddle. We are bad at solving riddles. It's more like hints about our favorite molecule. It is polar. And shaped like an elongated V. Its properties are amazing. It also makes up three-quarters of the Earth's surface. This hint always gives it away. Our favorite molecule is water. We won't lecture you about the importance of water and the fact that all life we know cannot survive without it, because yes, that's true, but we really want to talk about what makes water so unique to life itself. What are those amazing features? We mentioned the shape of water and the fact that it is polar. It has one highly electronegative oxygen that always tries to keep electrons closer to it than the hydrogen bonded to it. This gives the oxygen a relatively negative charge—because of the electrons spending more time near it—and gives the hydrogen a relatively positive charge.
This means that other water molecules can bond together easily. Why? Because the positively charged hydrogen atom in one water molecule can bond to the negatively charged oxygen atom of another water molecule. This bond between water molecules is a hydrogen bond, and these bonds are what allow water to do the things it can do... which is what we'll talk about. Have you ever looked at a tall tree and wondered, "How does water get to the top?" I mean, it's going against gravity. Gravity! In our plant video, we talked about xylem. These are vessels found in some plants, like trees, that transport water. But the cool thing about water is that—it sticks to the walls of the xylem by something called adhesion. This helps resist gravity. But water molecules, with their hydrogen bonds, stick to each other by something called cohesion. It's like beads on a string; when one water molecule evaporates from a leaf, the other water molecule in the string pulls it up. Cohesion is also the reason why a water strider can walk on water, one of our favorite insects, it can skate on water. Cohesion contributes to creating surface tension in water. In fact, water has a simple surface tension compared to other liquids. It's not just water striders that can do this. There are many insects, spiders, and even animals like reptiles and birds that can walk on water. Look them up more on Google. Because water is polar, it makes it a strong solvent. This means that water can dissolve many other molecules, especially polar and ionic ones. Why does that matter? It matters because many of the processes that happen inside our bodies use water as a solvent. Just think about the kidney's need for water for filtration and all sorts of bodily fluids. I will never forget when I was little, my dad built us a pond. We had some goldfish in it. We loved our pond. In West Texas, where we live—it can snow in the winter. And one day I went outside, terrified, to find that the surface of my pond had frozen. I thought my fish had died. Only to discover that they were still swimming and doing... fish activities... under the ice layer. Most compounds contract when they freeze and become denser. But water expands when it freezes and becomes less dense. This results in an ice floe that can create an insulating layer that makes a difference for many creatures. This is because of the hydrogen bond. At the freezing stage, breaking and reforming these bonds—which usually happens—not so much. The molecules are fixed in a network of hydrogen-bonded molecules far enough apart to be less dense in the ice state than in the water state. All of this will be important for aquatic life. Speaking of heat, water resists temperature change. It has what's called a high specific heat. Specific heat is a measure of the heat that must be absorbed or lost to change the temperature by one degree Celsius per gram of substance. So, on the first day of summer vacation, it might be very hot outside, but the water is still relatively cool. It's very good that water is like this for life—it makes the temperature of aquatic environments stable. It also means that water can absorb a lot of heat in the summer without reaching high temperatures itself—which is important when winter comes. Water can release heat as it cools. We're still on the topic of heat, let's mention evaporation. Many animals rely on evaporation to cool themselves. Think about water molecules. They are moving, but those with more energy—they are "hotter," for example—move faster. They are the ones most likely to change state to gas. When these molecules leave, their energy—their heat—is no longer on your skin. By the way, this isn't just for animals. Plants use evaporative cooling to help them in high heat. High temperatures can be dangerous for many different processes in both plants and animals—they can be harmful to enzymes in many of these processes. Well, we've gone over a lot of water's properties—definitely something to consider the next time you encounter water. Which, given how much we rely on it... will probably be soon. Well, that's all for the Amoeba Sisters, and we remind you to stay curious.